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Solid materials in the Solar System and atmospheric ozone

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Is there a link between the oldest solid materials in our solar system and atmospheric ozone?

This is a key issue for understanding the origin of our solar system. Is the isotopic composition of the oldest solids of our solar system due to a selective filtration of the young strong sunlight or a chemical reaction? According to the chosen process, the conclusions concerning the conditions of formation of the solar nebula are different, hence the importance of answering this question.  

The amazing correlation between refractory oxides in some meteorites, unique proof of the solar system formation 4.5 billion years ago, and ozone that protects us from UV radiation from the sun, has been postulated because of the very specific isotopic composition found in these two so different components. Indeed, almost all terrestrial materials show that isotopic ratios 17O/16O et 18O/16O (heavy and stable oxygen isotopes from the main isotope 16O) correlate well, whereas ozone and some components of meteorites do not follow this strictly and almost universal correlation. A common origin of these anomalies, particularly due to the process of adding a free oxygen atom in a diatomic molecule, seems plausible.

To test this hypothesis, researchers at the EMPA (Swiss Federal Laboratories for Materials Testing and Research, Dübendorf, Switzerland) in Switzerland and LPMAA (Molecular Physics for Atmospheric and Astrophysics Laboratory, UMR 7092, UPMC / CNRS / IPSL) in Paris have recently completed some work which started at the Max Planck Institute in Heidelberg (Germany). They have studied the possible link to watch the change in the isotopic composition of ozone formed in electrical discharges function of pressure and temperature. As the three-body reaction in the gas phase - classical reaction of ozone generation responsible for the isotope anomaly of this molecule by adding an oxygen atom to the diatomic molecule in the presence other molecules - is less competitive under a low pressure than the corresponding reaction on the walls, the researchers had the idea of reducing the pressure in their experiment. This approach allows to reach the probable oxidation process in the solar nebula. Indeed, because of the conditions of low pressure and high temperature of the nebula, the oxidation by free atom should occur on the surfaces of preexisting grains.

 The crux of this experiment was to distinguish the mechanism of ozone formation on the surfaces of the classical process of formation. This analysis is complex due to the simultaneous presence of ions and excited molecules and atom. It was achieved through the confrontation of a kinetic model with experimental measurements made under different conditions of pressure and temperature. The result is striking: the isotopic anomaly of ozone formed disappears on the walls. This observation is attributed to a vibration energy transfer which is highly effective on the surface.
 
Therefore, adding free atoms on surfaces does not seem to be capable of generating isotopic anomalies, in contrast to gas phase reactions where the formation of atmospheric ozone is an indicative example of isotopic abnormality caused by a chemical reaction. When it comes to refractory inclusions in meteorites, the result implies a common origin of anomalies in atmospheric ozone and the refractory oxides is unlikely. The origin of their composition must be sought elsewhere and the trail of a molecular dissociation varying with the isotope is more promising

 

Reference

Janssen, C., Tuzson, B.

Isotope Evidence for Ozone Formation on SurfacesNouvelle fenêtre J. Chem. Phys. A 2010, XX, DOI: 10.1021/jp1017899, Publication Date (Web):– Publié le 06 mai 2010.

 

Contact

C. Janssen, LPMAA

janssen@lpma.jussieu.fr

+33 1 44 27 96 72   

 

Isotopic composition of ozone as a function of pressure for temperatures (T) and ray (R) of different reactors.

 

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18/06/10